Anionic surface active agents, such as alkylbenzenesulfonates, have widely been used as main components in dishwashing detergents. From the viewpoint of irritation to the skin, the tendency now is turning toward mild detergents containing alkyl ether sulfates and amphoteric surface active agents as main components. However, alkyl ether sulfates are still unsatisfactory in mildness to the skin, and further improvements have been demanded.
It has been proposed to incorporate an N-acylamino acid salt which is not only mild to the skin but effective to inhibit growth of harmful microorganisms causing skin diseases as disclosed in JP-B-46-4256 and JP-B-39-29444 (the term "JP-B" as used herein means an "examined Japanese patent publication"). However, an aqueous solution of the N-acylamino acid salt per se has low detergent action and it lacks detergency and foamability for cleaning off extremely oily dirt, for example, dishes or hair applied with pomade.
JP-A-48-5904 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses use of an N-aclyglutamate in combination with a tertiary alkylamine oxide to thereby improve detergency and foamability without impairing mildness to the skin. However, it has been proved by the inventor's investigations that the tertiary alkylamine oxide must be used in an amount of at least 2/3 as much as the weight of the N-acylglutamate before one can obtain improved detergency and foamability and that incorporation of the tertiary alkylamine oxide in such a high ratio causes gelation and substantial loss of fluidity.